A Trend is the graphical representation of a Data Sample. Therefore, to implement a Trend graph, you must:
In addition to the standard Trend graph widget, where the X axis is time, you can create a graph using the XY Trend widget. This enables you to define units such as millibar or degrees for the X axis.
You can view a video tutorial on this subject on the following link:
http://www.youtube.com/watch?v=pSAm1HVvOO4&list=PLFBq_OH6_be7snAZAycZzQMvAWjHkX9Pz